FIG. 7 is a cross sectional view of a conventional acceleration sensor. As shown in FIG. 7, diaphragm 2 is formed in a rear side of chip 1, and a plurality of distortion sensing resistors 3 are disposed on a surface side of the chip, (i.e., an opposing side of the diaphragm from the rear side). At another portion of the surface side of chip 1, a semiconductor integrated circuit for computing acceleration, and thin film resistor 4 for adjusting performance of the semiconductor integrated circuit are disposed. Protection film 5 is formed on the surface side covering at least thin film resistor 4 but not covering distortion sensing resistors 3. On the rear side of chip 1, glass weight 6 is attached.
When acceleration is applied to this conventional acceleration sensor, a stress is applied to weight 6. The sensor then detects the acceleration with a deformation of distortion sensing resistor 3. When two axes detection is required, two identical sensors are disposed crossing with each other at right angles. An example of this type of conventional acceleration sensor is disclosed in Japanese Patent Unexamined Publication No. H5-288771 (JP '771).
Another example of this type of conventional sensor is disclosed in Japanese Patent Unexamined Publication No. H5-80075 (JP '075). FIG. 8 is a block diagram showing an example of the acceleration sensor. As shown in FIG. 8, the sensor is composed of piezoelectric element 11 outputting a signal corresponding to acceleration G, impedance converter 12 converting the signal output from piezoelectric element 11, filter 13 filtering an unneeded signal from the signal output from impedance converter 12, amplifier 14 amplifying a needed signal output from filter 13, alternating signal output device 16 outputting an alternating signal synchronized with a synchronism of a timing signal input from an outside, and capacitor 17 connected in series between alternating signal output device 16 and piezoelectric element 11.
A voltage signal output from this conventional acceleration sensor is input to measuring/operating unit 18 and controller 15. When two axes detection is required, two identical sensors are disposed crossing with each other at right angles for detection.
In the acceleration sensor in JP '771, a several percent of change in resistance value can be identified with a semiconductor resistor distortion formula. However, in this device, accurate acceleration detection is difficult because the variance in the change of the resistance value is wide and signals are affected by a change in the temperature of the processing circuits.
With the device in JP '075, where the piezoelectric element is used for detecting displacement speed of the element, detecting of such as a component of static gravitational acceleration is difficult because of its detecting mechanism. Two sensors are required for two axes detection. Thus, cost increase and possible variation in performance exist.